Problem description
Phone number optionally prefixed with '+' before hashing? Why is this an option?

    NumberVerificationRequestBody:
        ...
        hashedPhoneNumber:
          description: Hashed phone number. SHA-256 (in hexadecimal representation) of the mobile phone number in **E.164 format (starting with country code)**. Optionally prefixed with '+'.

This means that the supplied hashed phone number must be compared to two hashes of the true phone number to determine if they match. Some have claimed this is a "feature" for those who cannot read a specification or format phone numbers properly, but I think this is a bug that increases implementation complexity and processing time.

Expected behaviour
Adding '+' before hashing should be mandatory

    NumberVerificationRequestBody:
        ...
        hashedPhoneNumber:
          description: Hashed phone number. SHA-256 (in hexadecimal representation) of the mobile phone number in **E.164 format (starting with country code and mandatorily prefixed by '+')**

Alternative solution
Remove option for hashing completely. It adds no data security for such a small plaintext space.

Additional context